Tips for buying Mammography Unit

Facilities should base their
Mammography unit screening purchase decision on life-cycle cost, local
service support, discount rates and non-price-related benefits offered by
the supplier, and standardization with existing equipment.

Suppliers offer service
contracts or service on a time-and-materials basis. This may also be
available from a third-party organization. Facilities should carefully
consider whether to purchase such a service.

When purchasing a Mammography
screening equipment unit, performance and reliability are important
factors.

A Mammographic unit high-frequency
x-ray generator will help ensure higher efficiency of operation with a
minimum of output ripple. It will also need less space than a conventional
generator.

Mammography involves a narrow
range of tissue thickness, and therefore 1 kV increments and a range of
approximately 22 to 35 kV are necessary.

The system should offer at
least 500 mAs and an exposure time of 0.1 second or shorter to avoid
unnecessary long exposures.

A rotating anode, which has a
higher heat capacity than a stationary anode, should be available on the
Mammography unit to promote longer x-ray tube life and provide a more
consistent x-ray output.

Focal spot sizes should be
approximately 0.1-0.3 mm to ensure that micro calcifications as small as
200 µm can be detected.

To clearly image the smallest
micro calcifications, an SID of at least 66 cm is needed.

The complexity of the
automatic exposure control is the main difference between systems. Some
systems control only the exposure time, while more advanced ones control
the x-ray spectrum, including the kVp, anode, and filtration. Such systems
improve the image quality, especially in larger and denser breasts.

Some manufacturers of Mammography
units have developed advanced grids, which are expensive to manufacture
but improve the image quality.

Facilities considering the
purchase of a stereo tactic biopsy system should consider the number of
procedures to be performed and the compatibility with existing Mammographic
equipment.

Film-based Mammographic units
are not recommended because they do not allow real-time guidance. Instead,
both dedicated and add-on systems are equipped with small digital
detectors.

Add-on systems may be harder
to use because they have more limited motions compared to dedicated mammographic
systems. Consequently, most of the differences are a matter of user
preference rather than clinical efficacy.

In digital detector
performance, detective quantum efficiency is an important factor. DQE is
directly related to the signal-to-noise ratio that results between
detector input and output. The noise generated by the detector and the
spatial resolution contributes to the DQE of the system. To reduce DQE,
SNR must be reduced; a recommended DQE is less than 20% at 5 lp/mm.

Another important factor when
considering a purchase of a Mammography unit is modulation transfer
function. MTF refers to the loss of contrast relative to an x-rayed
object. As spatial frequencies in a given image increase, MTF decreases,
creating loss of visualization. A 50% MTF at 5 line pairs per
millimeter is recommended.